Wireless communication systems are known to include a plurality of wireless communication devices that communicate directly (e.g., point-to-point) or through an infrastructure. For direct communications, a wireless communication device, such as a radio, cellular telephone, station coupled to a personal computer or laptop, et cetera, transmits data on a particular radio frequency channel directly to another wireless communication device. For infrastructure-supported communications, a wireless communication device transmits data on an assigned radio frequency channel to an access point (or a base station). The access point determines the targeted wireless communication device from the received RF signals. If the targeted wireless communication device is affiliated with the access point, the access point transmits the data to the targeted wireless communication device on a radio frequency channel. If the targeted wireless communication device is not affiliated with the access point, the access point forwards the data to a central station, which routes the data to the access point that is affiliated with the targeted wireless communication device.
To ensure reliability of data transmissions within a wireless communication system and to ensure interoperability of differing manufacturers' equipment, standards have been developed. Such wireless communications standards include IEEE8 02.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution services (LMDS), multi-channel, multi-point distribution systems (MMDS), and/or variations thereof.
Such standards prescribe operating parameters for particular types of wireless communication systems. For example, the IEEE 802.11a standard defines a wireless local area network that prescribes a frequency band of use, division of the frequency band into channels and sub-channels, encoding/decoding convention, modulation/demodulation convention, frame format, data rates, et cetera. Further, the IEEE 802.11a standard provides various combinations of data rates and modulation schemes, which can be selected via a coding rate corresponding to a particular modulation scheme.
In such standard compliant systems, data is transmitted in a particular format such that the targeted wireless communication device, or devices, can accurately recover the transmitted data. For instance, many standards prescribe for the use of preambles to inform the targeted wireless communication device, or devices, that data is to come. As such, the receiver portion of the targeted wireless communication device, or devices, monitors baseband signals (i.e., a modulated RF signal that has been converted down to baseband) to determine if the baseband signals contain a valid preamble. If a baseband signal includes a valid preamble, the receiver processes the baseband signal to recapture the transmitted data. To determine whether the baseband signal includes a valid preamble, the receiver includes a correlator.
As is known, a correlator compares the incoming baseband signal to a stored representation of a valid preamble. If the beginning portion of the incoming baseband signal (e.g., the portion that would correlate to a preamble of a valid signal) matches the stored valid preamble, the correlator indicates that the signal is valid. Based on the correlator's indication, the remaining portions of the receiver are enabled to recover the data from the baseband signal.
If the correlator falsely identifies a valid signal, the subsequent processing by the receiver is wasted. For portable wireless communication devices, wasted receiver processing corresponds to wasted power, which reduces the battery life of a wireless communication device. Such false identifications occur more frequently as the signal strength of the received RF signal decreases. As such, many wireless communication devices have a minimum signal strength requirement to reduce the number of false identifications, but does so at the cost of limiting the range of the wireless communication device.
Therefore, a need exists for a method and apparatus that accurately detects the presence of a valid signal such that the range of wireless communication devices is extended, minimum signal strength requirements are reduced and/or eliminated, and/or power consumption of wireless communication devices is reduced.